JP2002194519A - METHOD FOR MANUFACTURING HOT-DIP Al-Zn ALLOY PLATED STEEL STRIP - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably manufacture a hot-dip Al-Zn alloy plated steel strip which is provided with a plating film containing Al of 20-95 mass%, has superior elongation characteristics, and moreover shows an attractive appearance. SOLUTION: The method for manufacturing the hot-dip Al-Zn alloy plated steel strip with improved elongation characteristics by heating the plated steel strip after plating metal is solidified, comprises coiling up the hot-dip Al-Zn alloy plated steel strip with the plated film having a surface roughness Ra (an arithmetic mean roughness specified in JIS) of 0.20 μm at a coiling-up tensile strength of 3.0 kg/mm2 or less, and heating a batch of the tight coil in such a condition that the strip temperature in the maximum temperature part of the coil reaches less than 300 deg.C; or, coiling up the hot-dip Al-Zn alloy plated steel strip, and heating a batch of the open coil in such a condition that the strip temperature in the maximum temperature part of the coil reaches less than 300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing A
The present invention relates to a method for producing a hot-dip Al-Zn-based plated steel sheet having an l content of 20 to 95 mass%.

[0002]

2. Description of the Related Art A hot-dip Al-Zn plated steel sheet (hereinafter referred to as "55% Al-Z-plated steel sheet" represented by a 55% Al-Zn-based steel sheet containing 20 to 95 mass% of Al in a plating film.
n-plated steel sheet) will be described as an example)
As shown in No. 161, it shows excellent corrosion resistance as compared with hot-dip galvanized steel sheet, and in recent years, demand has been increasing mainly in the field of building materials. This 55% Al-Zn-based coated steel sheet is prepared by pickling and descaling a hot-rolled steel sheet or a cold-rolled steel sheet obtained by cold-rolling the hot-rolled steel sheet as a base steel sheet. Manufactured.

In a continuous hot-dip plating apparatus, a base steel sheet is heated to a predetermined temperature in an annealing furnace maintained in a reducing atmosphere to remove rolling oil and the like adhering to the steel sheet surface simultaneously with annealing.
After the oxide film is reduced and removed, the lower end is immersed in a hot-dip galvanizing bath containing a predetermined concentration of Al through a snout immersed in the plating bath. After the steel sheet immersed in the plating bath is lifted above the plating bath via the sink roll, by injecting pressurized gas from the gas wiping nozzle placed on the plating bath toward the surface of the steel plate The amount of plating is adjusted, and then cooled by a cooling device to form a 55% Al
-A Zn-plated steel sheet is obtained.

The operating conditions such as the heat treatment conditions and atmosphere conditions of the annealing furnace in the continuous hot-dip plating equipment, the plating bath composition, and the cooling rate after plating are controlled within predetermined control ranges in order to ensure desired plating quality and material. Well managed. The plating film of the 55% Al—Zn-based plated steel sheet manufactured as described above is mainly composed of Al containing Zn in supersaturation.
Consists of dendrite solidified portions and remaining dendrite gap portions, and the dendrites are stacked in the thickness direction of the plating film. Due to such a characteristic coating structure, the 55% Al-Zn plated steel sheet exhibits excellent corrosion resistance.

[0005] In addition, usually about 1.5 mass% of Si is added to the plating bath.
The 5% Al-Zn plated steel sheet suppresses alloy phase growth at the interface between the plating film and the base steel sheet, and has an alloy phase thickness of about 1 to 2 μm.
It is about. The thinner the alloy phase, the greater the number of characteristic film structures exhibiting excellent corrosion resistance. Therefore, suppressing the growth of the alloy phase contributes to the improvement of the corrosion resistance. Usually, the plating bath contains unavoidable impurities, Fe eluted from steel plates and equipment in the plating bath, and Si for suppressing alloy phase.
In addition to these, some elements may be added, and these elements are present in the alloy phase or the plating film in the form of an alloy or a simple substance.

[0006]

As described above, 55%
Al-Zn plated steel sheet has excellent corrosion resistance,
Hot-dip Al-Z having mechanical properties, especially elongation properties, of other plated steel sheets, for example, about 5 mass% of Al in a plating film.
It tends to be inferior to n-type plated steel sheets (hereinafter referred to as "5% Al-Zn-based plated steel sheets"), and thus has a difficulty in being used for applications requiring severe processing. 5
% Al-Zn coated steel sheet is excellent in elongation characteristics and therefore easy to work, but is inferior in corrosion resistance as compared with 55% Al-Zn coated steel sheet.
% Al—Zn-based plated steel sheets are being replaced.

As described above, since the 55% Al-Zn coated steel sheet has a small elongation characteristic value, even when the same processing is performed, compared with a 5% Al-Zn coated steel sheet having the same plating film thickness. It tends to be poor. Therefore, when processing such as bending is performed, cracks may occur in the plated steel plate portion of the processed portion depending on the degree of processing, which may cause a serious problem in use. For such a problem, for example,
No. 1-2748 describes a method of improving the ductility by subjecting a 55% Al—Zn-based plated steel sheet to a predetermined heat treatment. However, the present inventors have confirmed through experiments and the like that when such heat treatment is performed on a plated steel sheet coil by batch processing, seizure (adhesion) occurs between the steel sheets in the coil during the heat treatment. It has been found that this causes a problem that the beautiful surface appearance of the plated steel sheet as a product is significantly impaired.

Japanese Patent Publication No. 53-9176 discloses that a galvannealed steel sheet is batch-annealed to 400-48.
When heating to 0 ° C., a method is described in which the heating atmosphere is made slightly oxidizing to prevent seizure between steel sheets.
When batch heating of an Al—Zn-based plated steel sheet is performed in the above temperature range, occurrence of seizure between the steel sheets cannot be avoided. Therefore, an object of the present invention is to reduce the Al content in a plating film, which is represented by a 55% Al—Zn plated steel sheet, to 20 to 9%.
A hot-dip Al-Zn-based plated steel sheet having a mass of 5 mass%,
Molten Al-Z capable of stably producing plated steel sheets having excellent elongation characteristics and a beautiful plated surface appearance
An object of the present invention is to provide a method for producing an n-type plated steel sheet.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the elongation characteristics of a 55% Al—Zn-based plated steel sheet from the viewpoint of securing an excellent plated surface appearance as a practical product. The present inventors have conducted intensive studies on an optimum manufacturing method for improving the appearance and obtaining a beautiful plating surface appearance. As a result, when a 55% Al—Zn-based plated steel sheet is manufactured in a continuous hot-dip plating line, a plating film having a plating surface roughness Ra of 0.20 μm or more is formed,
Heating is performed by reducing the winding tension during coil winding to 3.0 kg / mm ² or less, and then performing tight coil batch heating under conditions such that the ultimate plate temperature at the coil maximum temperature section is less than 300 ° C. Appropriate improvement of elongation characteristics by the treatment is achieved, and baking between plated steel sheets in the coil is appropriately prevented, and a 55% Al-Zn-based coated steel sheet having excellent elongation characteristics and a beautiful plated surface appearance can be manufactured. I understood.

When the above heat treatment is carried out by open coil batch heating, the heat treatment is carried out under such conditions that the ultimate plate temperature at the highest temperature portion of the coil is less than 300 ° C., so that the elongation characteristics are excellent and beautiful. It was found that a 55% Al-Zn-based plated steel sheet having a plated surface appearance could be manufactured. That is, the method for producing a hot-dip Al-Zn plated steel sheet of the present invention has the following features.

[1] The Al content in the plating film is 20 to 9
A method for producing a hot-dip Al-Zn-based coated steel sheet having a mass of 5 mass%, wherein a heat treatment is performed on the hot-dip Al-Zn-based coated steel sheet after solidification of the plated metal to improve the elongation characteristics. Ra is 0.20 μm
After winding a hot-dip Al-Zn-based plated steel sheet on which the above-mentioned plating film has been formed at a coil winding tension of 3.0 kg / mm ² or less, the ultimate sheet temperature at the highest temperature portion of the coil is less than 300 ° C. by tight coil batch heating. A method for producing a hot-dip Al-Zn-based plated steel sheet, characterized by performing a heat treatment under the following conditions.

[2] The Al content in the plating film is 20 to 9
A method for manufacturing a hot-dip Al-Zn-based coated steel sheet having a mass of 5 mass%, wherein the hot-dip hot-dip coating of the hot-dip Al-Zn-based coated steel sheet after solidification of the plated metal improves the elongation characteristics. After winding a Zn-based plated steel sheet around a coil, a hot-dip Al-Zn-based plated steel sheet is subjected to a heat treatment by open coil batch heating under conditions such that the ultimate sheet temperature at the highest temperature of the coil is less than 300 ° C. Manufacturing method. [3] The method according to the above [1] or [2], wherein the oxygen concentration in the heating atmosphere when the coil is subjected to heat treatment by tight coil batch heating or open coil batch heating is 20% by volume or more. For producing a hot-dip Al-Zn-based plated steel sheet.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A plated steel sheet to be manufactured by the present invention is a hot-dip Al-Zn-based plated steel sheet containing 20 to 95 mass% of Al in a plated film, and a more preferable component composition of the plated film. Is Al: 45 to 65 mass
%, Si: 0.7 to 2.0 mass%, Fe: less than 10 mass%, the balance being substantially Zn containing unavoidable impurities,
In such a composition, particularly excellent corrosion resistance is exhibited.
The coating weight of the hot-dip Al—Zn-based coated steel sheet is not particularly limited, but is generally 30 to 120 g / side per side.
about m ² is appropriate.

According to the first method of the present invention, in a continuous hot-dip galvanizing line, the surface of a steel sheet has a plating surface roughness Ra of 0.20.
A molten Al-Zn-based plating film having a thickness of at least μm is formed, and the molten Al-Zn-based plated steel sheet is wound at a coil winding tension of 3.0 kg / mm ² or less. The heat treatment is carried out under such a condition that the reached plate temperature is less than 300 ° C.

Here, the reason why the plating surface roughness Ra of the hot-dip Al—Zn-based plated steel sheet is 0.20 μm or more is that when the plating surface roughness Ra is less than 0.20 μm, the plated steel sheet is wound around a coil. This is because the contact area between the plated steel sheets becomes large, seizure occurs between the plated steel sheets during the heating of the tight coil batch, and a plated surface appearance that can withstand use as a product cannot be obtained. However, if the value of the plating surface roughness Ra is too large, the unevenness of the plating surface becomes large and the plating surface appearance tends to deteriorate. Therefore, the plating surface roughness Ra is preferably set to 2.0 μm or less.

Factors that control the plating surface roughness Ra include the penetration temperature of the steel sheet into the plating bath, the plating bath temperature, the plating bath composition, and the like. In the case of a plated steel sheet which makes the spangle pattern inconspicuous, for example, the conditions of temper rolling after plating can be mentioned. Therefore, by appropriately adjusting these, the plating surface roughness Ra can be reduced to 0.2.
A plating film of 0 μm or more can be obtained.

Further, when the coated steel sheet is wound around the coil in the continuous hot-dip galvanizing line, the coil winding tension is set to 3.
0 kg / mm ² or less is when the winding tension is 3.0 k
If g / mm ² is exceeded, the contact force between the plated steel sheets in the coil increases, seizure occurs between the plated steel sheets during tight coil batch heating, and a plated surface appearance that can withstand use as a product cannot be obtained. That's why. However, if the coil winding tension is too low, the force for maintaining the coil state is weakened, and the coil is likely to be deformed or crushed. For this reason, the coil winding tension is preferably set to 0.3 kg / mm ² or more.

The coil of the plated steel sheet taken out from the continuous hot-dip galvanizing line is subjected to heat treatment by tight coil batch heating under conditions such that the ultimate sheet temperature at the highest temperature portion of the coil is less than 300 ° C., preferably 20 ° C. or less. . In this heat treatment, the ultimate plate temperature of the coil maximum temperature part is 300
If the temperature is higher than ° C., the viscosity of the plating surface decreases, seizure occurs between the plated steel sheets, and a plating surface appearance that can withstand use as a product cannot be obtained. It is appropriate that the lower limit of the heating temperature is such that the ultimate plate temperature at the lowest temperature portion of the coil is 100 ° C. or higher, preferably 150 ° C. or higher. If the ultimate plate temperature at the lowest temperature portion of the coil is less than 100 ° C., the effect of improving the elongation characteristics by heating cannot be sufficiently obtained.

It is appropriate that the heating and holding time is 5 minutes or more and 24 hours or less. If the heating holding time is less than 5 minutes, a sufficient elongation property improving effect cannot be obtained, while if it exceeds 24 hours, seizure between the plated steel sheets tends to occur. FIG. 1 shows a typical temperature rise / hold / cooling temperature pattern of tight coil batch heating performed in the present invention.

The heating atmosphere for performing the tight coil batch heating may be air, N ₂ , H _2, or N ₂ -H ₂ . However, if the atmosphere contains oxygen, a thin oxide film is formed on the surface of the plating film during heating, and this oxide film works advantageously to prevent seizure between the steel sheets. From such a viewpoint, it is preferable that the atmosphere of the heat treatment contain 20% by volume or more of oxygen.

In the second method of the present invention, a hot-dip Al-Zn-based coated steel sheet produced in a continuous hot-dip galvanizing line is wound into an open coil state, and the maximum sheet temperature at the coil maximum temperature portion is 300 ° C. by open coil batch heating. The heat treatment is carried out under such a condition as to be less than. In the second method of the present invention, since the coil is subjected to the heat treatment in the open coil state, the plating surface roughness Ra is not limited as in the first method. In addition, since the wound coil is placed in an open coil state before the heat treatment, the winding tension when winding the plated steel sheet around the coil is not limited as in the first method.

The coil of the plated steel sheet taken out of the continuous hot-dip galvanizing line is subjected to heat treatment by open coil batch heating under conditions such that the ultimate sheet temperature at the highest temperature portion of the coil is less than 300 ° C., preferably 200 ° C. or less. . The reason for limiting the heating temperature, the preferable conditions of the heat treatment, the atmosphere, and the like are the same as in the first method described above. Also,
Typical temperature rise / hold /
The cooling temperature pattern is the same as in FIG.

The plated steel sheet produced by the method of the present invention comprises:
A spangle may be formed on the plating surface, or a spangle pattern may be made inconspicuous. In general, a plated steel sheet having a spangle on a plating surface is suitable for use in which the spangle is unobtrusive because of its appearance, and a plated steel sheet in which the spangle pattern on the plating surface is made inconspicuous is suitable for use as an undercoat. In order to make the spangle pattern on the plating surface inconspicuous, temper rolling or the like may be performed after plating according to a conventional method.

[0024]

[Example 1] A cold-rolled steel sheet (sheet thickness: 0.5 mm) manufactured by a conventional method was passed through a continuous hot-dip plating apparatus to obtain 55 ma.
Hot-dip plating was performed using an ss% Al-1.5mass% Si-Zn plating bath to produce a hot-dip Al-Zn plated steel sheet, which was wound around a coil. The line speed of the hot-dip plating line was set to 160 m / sec, and the single-sided plating adhesion amount was set so that the variation between the plated steel sheets was within the range of 75 to 90 g / m ² . Next, the plated steel sheet coil was heat-treated under various conditions by tight coil batch heating to obtain a product of a molten Al-Zn-based plated steel sheet.

The obtained product was evaluated for the occurrence of baking, the appearance of the plated surface, and the elongation characteristics according to the following methods. The results are shown in Tables 1 and 2 together with the hot-dip plating conditions, tight coil batch heating conditions, and the configuration of the plating film. In each of the examples (Examples of the present invention and Comparative Examples) shown in Table 1, a tempered rolling was performed before heating the tight coil batch to obtain a plated steel sheet in which the spangle pattern on the plating surface was made inconspicuous. In each of the Examples (Examples of the present invention and Comparative Examples), plated steel sheets having spangles on the plating surface were manufactured.

(1) Presence or absence of seizure During the rewinding of the coil after the heat treatment, the presence or absence of seizure was evaluated as follows based on the presence or absence of sound generated when the coated steel sheets peeled off. None: No squealing noise is generated when rewinding the coil. Occurrence: A crunch sound is generated when the coil is unwound.

(2) Plating Surface Appearance The surface appearance of the plated steel sheet after the heat treatment was visually observed and evaluated as follows. Good: The plating surface has no change from that before the heat treatment and has a beautiful plating surface appearance. Poor: Plating exfoliation or welding occurs due to baking between plated steel sheets in a portion of 1% or more of the total coil area, resulting in poor plated surface appearance.

(3) Elongation Characteristics JIS Z 2201 (1998) Using a No. 5 test piece specified in a tensile test piece for a metal material, a JIS Z 224 test piece was used.
1 (1998) A test was conducted in accordance with the tensile test method for metallic materials, and evaluated by the total elongation at break. As a specific evaluation method, evaluation was performed based on the increase (%) of the total elongation at break relative to the total elongation at break of the plated steel sheet before performing the heat treatment.

[0029]

[Table 1]

[0030]

[Table 2]

[Example 2] A cold-rolled steel sheet (sheet thickness 0.5 mm) manufactured by a conventional method was passed through a continuous hot-dip plating apparatus, and 55
Hot-dip plating was performed using a mass% Al-1.5mass% Si-Zn plating bath to produce a hot-dip Al-Zn-based plated steel sheet, which was wound around a coil. The line speed of the hot-dip plating line was set to 160 m / sec, and the single-sided plating adhesion amount was set so that the variation between the plated steel sheets was within the range of 75 to 90 g / m ² . Next, the plated steel sheet coil was subjected to heat treatment under various conditions by open coil batch heating to obtain a product of a molten Al-Zn-based plated steel sheet.

With respect to the obtained product, the presence or absence of baking, the appearance of the plated surface, and the elongation characteristics were evaluated in the same manner as in [Example 1]. The results are shown in Table 3 together with the hot-dip plating conditions, open coil batch heating conditions, and the configuration of the plating film. In each of the examples (Examples of the present invention and Comparative Examples) shown in Table 3, a plated steel sheet having no spangle on the plating surface was manufactured by performing a skin pass before heating the open coil batch.

[0033]

[Table 3]

[0034]

As described above, according to the method of the present invention, 5
Hot-dip Al-Z having an Al content in the plating film of 20-95 mass%, as represented by a 5% Al-Zn-based plated steel sheet
It is possible to stably produce an n-type plated steel sheet having excellent elongation characteristics and a beautiful plated surface appearance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing typical heating, holding and cooling temperature patterns of tight coil batch heating and open coil batch heating performed in the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko Oi 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Kazuki Tachibana 1-1-2 Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. F-term (reference) 4K027 AA02 AA05 AA22 AB02 AB15 AB48 AC72 AE18 AE23

Claims (3)

[Claims] An aluminum content in a plating film is 20 to 95.
A method for producing a hot-dip Al-Zn-based plated steel sheet having a mass% of which is obtained by heat-treating a hot-dip Al-Zn-based coated steel sheet after solidification of a plated metal to improve elongation characteristics. After winding a hot-dip Al-Zn-based plated steel sheet on which a plating film having a Ra of 0.20 μm or more is formed at a coil winding tension of 3.0 kg / mm ² or less, the coil reaches the highest temperature part by heating a tight coil batch. Sheet temperature is 3
A method for producing a hot-dip Al-Zn-based plated steel sheet, comprising performing heat treatment under a condition of a temperature of less than 00C. 2. An aluminum content in a plating film of 20 to 95.
A method for producing a hot-dip Al-Zn-based coated steel sheet having a mass% of 1% by mass, comprising: After winding the Zn-based plated steel sheet around the coil,
A method for producing a hot-dip Al-Zn-based coated steel sheet, comprising performing heat treatment under conditions such that the ultimate sheet temperature at the coil maximum temperature section is lower than 300 ° C by open coil batch heating. 3. The molten Al according to claim 1, wherein the oxygen concentration in the heating atmosphere when the coil is subjected to heat treatment by tight coil batch heating or open coil batch heating is 20% by volume or more. -A method for producing a Zn-based plated steel sheet.